UGO.com spent a little time with Avatar: The Last Airbender creators, Michael Dante DiMartino and Bryan Konietzko. They grilled them on some details about the upcoming Nickelodeon series. Here are some highlights from the article:

The show will be a mini-series with little to no filler episodes with the two creators writing each episode.
We will see Aang in the show, but it sounds like he won’t be alive, which shouldn’t be a surprise.
They are sticking to having only one avatar alive at a time (which is good because thats central to the mythos)
Aang’s son, Tenzin, will be in the show (We know this from the release, he’ll be the airbending teacher for Korra)
Katara is, indeed, the mother of Aang’s son.
Airbenders will be under persecution in a way.
The story will not center around a war, but a different type of conflict.
Cheesy teen romance? Check.

Thats about it. For the full article, you can go here.